In the related art, for example, Japanese Unexamined Patent Application Publication No. 2000-168627 discloses a vehicle underbody structure that efficiently absorbs energy in a side collision. The vehicle underbody structure has a Z-shaped portion in a cross member, which is positioned in the vicinity of a tunnel portion of a floor panel, and thus the vehicle underbody structure suppresses an occurrence of a moment in a center pillar in a side collision, and absorbs energy.
When a collision load is exerted on the center pillar and the like, a rotational moment about a longitudinal axis is exerted on a rocker (a side sill) that is joined with a lower portion of the center pillar, and a torsional deformation occurs so that an upper portion of the rocker collapses inward in a width direction of a vehicle body. When the torsional deformation is increased, a rotational deformation, by which the center pillar collapses inward in the width direction of the vehicle body, is increased, and thus a collision performance of the vehicle underbody structure in a side collision cannot be satisfactorily ensured.